Solid propellant compositions have been developed which possess a wide range of chemical and mechanical properties that meet a wide range of performance parameters. Additive compounds for propellants have played a vital role in achieving these chemical and mechanical properties.
In recent years carborane chemistry as applied to solid propellant technology has been of particular interest. N-hexylcarborane which is prepared by the reaction of a decaborane ligand with n-octyne is a preferred carborane additive compound for propellant use. The decaborane ligands which have been most widely used are acetonitrile and diethylsulfide; other decaborane ligands can be prepared or selected from those reported in the literature.
N-hexylcarborane (NHC) is used in solid rocket propellants as a ballistic modifier and as a plasticizer to improve propellant mechanical properties. The cost to achieve these mechanical properties are quite high because of the limited production since at present there are no major commercial applications for the boron derivatives and carboranes. Present estimates indicate that the production cost of NHC will be as much as $400.00 per pound compared to the conventional propellant ingredients which cost in the order of $1.00 to $5.00 per pound. Although the NHC is used in relative small quantities, it has a very significant influence on the cost of the propellant because of its unusually high cost.
In the manufacture of solid rocket propellants, there is always some waste/scrap propellant along with some rejected motors. Because of the high cost of the NHC, methods to recover the NHC need to be developed and demonstrated to provide data to show that it is economically feasible and worth while to recover NHC for reuse. Recovery of NHC could be obtained from waste propellant, propellant test specimen, reject motors and rejected propellant, both cured and uncured material.
The recovery of carborane from reject propellant and motors could offer an advantage in the reduction of the manufacturing cost of missiles. For the recovery process to be an effective cost saving operation, the carborane must be recovered and purified for reuse. The cost of the operation must be such that the recovered carborane is much cheaper than the carborane obtained from production.
An object of this invention is to provide a process for the recovery of carborane from reject propellant from various sources including waste propellant, propellant test specimen, and reject motors, both cured and uncured materials.
A further object of this invention is to provide a process particularly adapted for the recovery of a preferred carborane, n-hexylcarborane, from reject propellant.
Another object of this invention is to provide a process which includes provisions for recycling the extraction solvent compounds employed to recover the carborane compound to thereby improve the cost effectiveness of the overall process.